At least one and possibly all five towers at the massive Riverside Center development will not be the work of Pritzker Prize-winning architect Christian de Portzamparc. The French designer helped Extell Development and the Carlyle Group sell their swank plans‘ to the community and the City Planning Commission. The latter was so taken with the crystalline designs of Mr. de Portzamparc, who also designed the LVMH headquarters and Extell’s One57 tower, that restrictive zoning covenants were set to ensure the buildings would look as promised.

But now, Extell and Carlyle have turned over one of their tower sites to the Dermot Company, which has hired local firm SLCE to design the apartment building on the West End Avenue section of the site. While Dermot insists its project will be up to the standards promised during last year’s public review process, some, including the exacting City Planning chair Amanda Burden, worry the design doppelgangers will lead to lesser work.

“I am extremely disappointed to learn that the developer of Riverside Center has chosen not to retain Christian de Portzamparc as architect for this project,” Ms. Burden said in a statement.

When Dermot came to the local community board last month to present its version of the designs, there was some disappointment that they had not been joined by Mr. de Portzamparc. “If you look at it, they’re more usual, they’ve probably been value-engineered,” Ehtel Shefer, chair of the board’s Riverside Center working group, told The Observer in a phone interview. “I don’t know if it’s the feeling of the entire board, but certainly some people were disappointed.”

Back in 2005, Carlyle and Extell bought the remaining undeveloped portion of Donald Trump’s Riverside South development from his Hong Kong partners (to the consternation of Mr. Trump) for $1.76 million. Much of it has since been developed as new towers by Gary Barnett, Extell’s principal, but the southernmost parcel had to be rezoned because previous plans called for a new television studio to be built on the site.

When it came time to start building, Carlyle, which controls a majority stake in the site, decided to hold a competitive bidding process, to which Extell was invited but not guaranteed the chance to build the first tower. Instead, the prize went to Dermot. When it comes time to build the remaining four parcels, Carlyle expects to go through the same private bidding process.

Mr. Barnett said that given the large amount of affordable housing and the school in the first building, he was less interested in winning the project. He still hopes to take the lead on some, if not all, of the other development sites, though he acknowledged there was no guarantee any of the towers would be his to build.

“I hope we get to build some, but I don’t know,” he said. “If we do, I can tell you, Christian de Portzamparc will be our architect.”

Carlyle declined to comment.

Councilwoman Brewer was ambivalent about the changes. “I was more concerned with the school and the affordable housing, but I can see why people might be angry about this,” she said, adding that of Mr. de Portzamparc, “They certainly made a hard sell for him during the ULURP.”